1. Field of the Invention
The present invention relates to the design and manufacture of semiconductor devices, in particular, a method of and apparatus for cooling a semiconductor chip in an electronic package.
2. Description of Related Art
Thermal management is a key issue in the design of the electronic package. The proper design insures that the peak temperatures remain within a specified operating range to produce a reliable module. The main objective is to maintain the semiconductor device junction temperature below the maximum operating temperature of the module. Design challenges included in heat removal are higher circuit densities, close proximity of adjacent devices or components, low thermal conductivity substrates, inner layers of metal forming the interconnect, and the thermal resistance of heat sink systems.
The purpose of any heat transfer design is to allow the flow of thermal energy from heat source to heat sink within the constraints of specified temperature levels. In the case of high performance machines, the burden of cooling has been shifting from the system level to the component level. Multi-chip modules having an increasingly close placement of components having high heat fluxes means that the various thermal resistances, from the internal heat sources to the external final heat sink, must be reduced. The prior art is replete with cooling mechanisms utilizing different mediums of heat exchange including liquids or solids, as discussed below.
U.S. Pat. No. 5,325,913 issued to Altoz discloses an apparatus used for cooling electronic components. The apparatus comprises of a heat sink enclosure having a wick bonded to the inside surface of the cavity of the enclosure. The enclosure has a plug containing a meltable pellet such that a working fluid is sealed inside a cavity of the enclosure permeates the wick. When the pellet melts, a vapor of the working fluid travels through the passage in the plug, thereby cooling the enclosure by releasing the vapor. However, the apparatus of this reference is considerably limited by the internal resistance between the component and the heat-sinking closure since the heat must flow from a chip through the substrate, heat sink, and wick in order to vaporize the working fluid within the heat sink enclosure.
U.S. Pat. No. 5,219,020 to Akachi discloses the structure of a heat pipe-type cooling mechanism for attachment to the surface of a heat sink. The heat dissipation contribution of the heat pipe-type mechanism reduces only the external resistance. The reference neither suggests nor discloses cooling semiconductor chips directly.
U.S. Pat. No. 5,024,264 to Natori et al. discloses a method of cooling a semiconductor devise with a cooling unit using a metal sherbet, a metal in liquid and solid phases, as a heat conducting body placed between a cooling unit and a heat generating devise. This reference uses conduction as a heat transfer means through a semi-liquid alloy which has limited cooling capacity for a semiconductor chip.
U.S. Pat. No. 5,199,165 to Crawford et al. discloses a heat pipe apparatus using a fluid phase change chamber in thermal contact with two or more electronic components. However, there is a great deal of thermal resistance across package layers, interconnects, and interfaces from the chip or component to the substrate, which limits the rate at which the heat can be dissipated despite the efficiency of the heat pipe mechanism.
U.S. Pat. No. 4,519,447 to Wiech, Jr. discloses a substrate cooling system using heat pipes and a bi-phase liquid metal such as mercury for the working fluid. Heat from the electrical component is transmitted from the substrate or chip to the heat sink. The working fluid in the vapor phase is transported along the continuous closed path of the cooling system. The cooling process is effected by the heat pipes or conduits which run on or within the substrate. However, the pipes must be in contact with the substrate or chip to extract the heat through liquid vaporization. Due to the internal resistance through many interfaces and the long piping system, the cooling process is not as efficient.
U.S. Pat. No. 4,104,700 to Hutchison et al. discloses a cooling system utilizing heat pipes attached to the frame or supporting carrier for the integrated circuits. Again as in other prior art cooling mechanisms using heat pipes, the limitation of multiple resistances along the heat path limit the heat removal efficiency.
U.S. Pat. No. 3,971,435 to Peck discloses yet another heat pipe cooling system. The cooling mechanism disclosed is applicable to substrates and cards which contain or require contact interfaces. The battery of thermal resistances severely limit the heat dissipation rate. This reference neither suggests nor discloses a method of directly cooling the chip within the electronic package.
Bearing in mind the problems and deficiencies of the prior art, it is therefore a object of the present invention to provide a method and apparatus for directly cooling a semiconductor chip in an electronic package.
It is another object of the present invention to provide a method and apparatus with low heat resistance between a heat source and a cooling unit in an electronic package.
It is yet another object of the present invention to provide a cooling system that would improve the heat dissipation of high power modules.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.